The meteor explosion over Russia that injured more than 500 people and damaged hundreds of buildings was not caused by an asteroid zooming close by the Earth Friday afternoon, a NASA scientist says.

NASA asteroid expert Don Yeomans, head of the agency’s Near-Earth Object Program Office, told SPACE.com that the object which exploded over a thinly inhabited stretch of eastern Europe today was most likely an exploding fireball known as a bolide.

More than 500 people were injured, mostly by glass cuts when windows shattered during the blast, according to the Russian Emergency Ministry.

“If the reports of ground damage can be verified, it might suggest an object whose original size was several meters in extent before entering the atmosphere, fragmenting and exploding due to the unequal pressure on the leading side vs the trailing side (it pancaked and exploded),” Yeomans told SPACE.com in an email. “It is far too early to provide estimates of the energy released or provide a reliable estimate of the original size.”